Definition of Period

A period is the name given to a horizontal row of the periodic table.

The periodic table has seven periods.

Apart from period 1, every period begins with an alkali metal and ends with a noble gas.

Period 1 contains only two elements: hydrogen and helium. Periods 6 and 7 are the longest periods, each containing 32 elements. Period 6 includes the lanthanides running from lanthanum to lutetium. Period 7 includes the actinides running from lanthanum to oganesson).

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